Synthesis of Sea Level During the Penultimate Interglacial

Research School of Earth Sciences, The Australian
National University,
Canberra, ACT, Australia, andrea.dutton@anu.edu.au

Over the past decade a
number of new sea level archives have greatly enhanced our knowledge of the
magnitude and timing of sea level changes during the penultimate interglacial,
also known as marine isotope stage (MIS) 7. Direct markers of sea level position before
the last interglacial period are generally rare owing in part to physical
overprinting of features during the last interglacial and Holocene highstands
in tectonically stable areas.This
physical overprinting is particularly problematic for elucidating evidence of
former highstands at similar elevations, such as during MIS 7 which reputedly
had at least one, if not more, sea level highstand(s) near present sea
level.In contrast, uplifting
coastlines, such as those found at Huon
Peninsula or Barbados, may
record spectacular geomorphological features (in this case coral terraces) that
formed during the penultimate interglacial.However, reconstructing the elevation of sea level in these tectonically
active areas is complicated by assumptions regarding the rate—and uniformity in
rate—of uplift.The magnitude of
uncertainty in sea level elevation in uplifting areas therefore increases the
further back in time these rates of uplift are extrapolated.

In addition to these challenges in determining the
elevation of sea level during the penultimate interglacial, the chronology of
sea level oscillations during this period of time has been historically
hampered by diagenetic alteration of datable material such as fossil
corals.Although the deterioration of
coralline aragonite has led to open-system behavior of the U-Th isotope system
in most MIS 7 corals that have been studied, a handful of ‘reliable’,
high-precision data do exist and modeling of open-system behavior has allowed
for a the construction of a significantly richer dataset.Alternative sources of data have also been
sought, and recent contributions from the dating of aragonitic sediments in
cores from the Bahamas and
of submerged speleothems in Italy
have added significant chronological constraints on the timing of sea level
highstands during MIS 7.

This
presentation will focus on providing a synthesis of sea level data across the
entirety of MIS 7, highlighting where discrepancies and gaps in the data exist
and where significant contributions can be made.Existing sea level data will also be compared
to more continuous models and reconstructions of sea level across this interval
to determine which of these reconstructions agrees best with the data—and why.Finally, some analysis of climatic changes
and forcing mechanisms will be included to give a more complete picture of the
current state of our understanding of climate dynamics and sea level change
during the penultimate interglacial.